Uninterceptable cruise missile.
It would be faster than the usual air defense SAMs (like S300 or Patriot) and AAMs.
You would need something approaching the performance of an ABM capable SAM, but those are designed for ballistic missile intercepts. This ramjet cruise missile would be a maneuvering target.
I am pretty sure a head-on intercept is an “easy” target solution (for vastly complex mathematics involved in a target solution). Sharp maneuvers and even the slightest amount of damage would cause it to break up.
Gets a lot harder if your are the Aegis destroyer trying to protect a carrier, though.
The primary advantage would be reaction time. Ships can only guide limited number missiles at a time. By the time one missile goes into terminal homing against these monsters, you won’t have a chance to engage the next. So, if your ship can guild eight missiles, and they launch nine...
By the time it's fielded, anti-air lasers will be available. And the plasma front on that thing will NOT be stealthy.